Why Doesn't ObservableCollection Detect Changes in Child Properties?

Addressing ObservableCollection's Limitations with Child Property Changes

The standard ObservableCollection in C# only tracks additions and removals of items. It doesn't inherently monitor changes to the properties of those items, even if those items implement INotifyPropertyChanged. This leads to UI bindings not updating when a child property is modified.

Enhanced ObservableCollection: The Solution

To solve this, we can create a custom collection class, let's call it TrulyObservableCollection, that extends ObservableCollection's functionality:

public sealed class TrulyObservableCollection<T> : ObservableCollection<T>
    where T : INotifyPropertyChanged
{
    public TrulyObservableCollection() : base() { }

    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Add)
        {
            foreach (T item in e.NewItems)
            {
                item.PropertyChanged += ItemPropertyChanged;
            }
        }
        else if (e.Action == NotifyCollectionChangedAction.Remove)
        {
            foreach (T item in e.OldItems)
            {
                item.PropertyChanged -= ItemPropertyChanged;
            }
        }
        base.OnCollectionChanged(e);
    }

    private void ItemPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Replace, sender, sender, IndexOf((T)sender)));
    }
}

This improved class ensures that when items are added, it subscribes to their PropertyChanged events. When a property changes, the ItemPropertyChanged method triggers a Replace action in the collection, effectively notifying bound UI elements of the change. Removal of items properly unsubscribes from the PropertyChanged event to prevent memory leaks.

Using TrulyObservableCollection guarantees that changes to both the items themselves and their properties are reflected in your data bindings, resulting in a more responsive and accurate UI.

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